In order to realize services aimed at improvements in safety, transport efficiency, comfort, etc., the development of an intelligent transport system (ITS) in which roads and vehicles are integrated together as a whole system has been promoted. The ITS is intended to realize such services by means of road-to-vehicle communication that is performed between a base station installed on a road and a mobile station mounted onto a vehicle or vehicle-to-vehicle communication that is performed between mobile stations.
Here, if an attempt is made to use the same communication scheme between the road-to-vehicle communication and the vehicle-to-vehicle communication for the purpose of effective use of limited frequency resources or the like, there is a risk that the communication schemes used in the two communications affect each other. In view of the above, there is disclosed a technology that enables avoiding interference from the vehicle-to-vehicle communication in a road-to-vehicle communication area by allocating a slot of a communication frame used for the road-to-vehicle communication, which is allocated to a predetermined mobile station, for communication with another mobile station that desires to perform the vehicle-to-vehicle communication with the predetermined mobile station (for example, see Patent Document 1).
Further, there is disclosed a technology of simultaneously transmitting, in polling performed between mobile stations and a base station, a polling instruction signal used for the polling and a predetermined collision control signal for avoiding a collision of polling actions in order to avoid the collision of the polling actions intended for the mobile stations and, at the same time, to minimize a time period required for the polling (for example, see Patent Document 2).    Patent Document 1: Japanese Laid-open Patent Publication No. 2000-165314    Patent Document 2: Japanese Laid-open Patent Publication No. 11-69441    Patent Document 3: Japanese Laid-open Patent Publication No. 2006-182207
In the above-mentioned road-to-vehicle communication and vehicle-to-vehicle communication, the communication schemes are conventionally separated from each other. Due to this, the use of frequency resources is not necessarily efficient. Meanwhile, if both the communication schemes are to be implemented in the same frequency band, it may be necessary to secure the frequency resources so as to prevent a collision of the communication actions. Considering this fact from a broader point of view, efficient utilization of frequency resources and avoidance of a collision are a significantly important challenge for communication performed among communication nodes, such as a plurality of mobile stations.